This invention relates to the art of stands for metal working machines and, more particularly, to a foldable stand for a power driven threading machine.
The use of portable power driven pipe and rod threading machines to facilitate the on site preparation of threaded pipe and rod is of course well known, and it is likewise well known to provide a stand to support such a machine during metal working operations. Certain such stands for the latter purpose have been foldable and comprised of a scissors-like leg assembly having ground engaging wheel and handle components and which stands are adapted to be displaced between the folded and unfolded positions with the metal working machine mounted thereon. Such folding and unfolding has been achieved heretofore, for example, by a mechanical spring loaded counterbalance arrangement, or through the use of a crank actuated screw arrangement. When folded, the wheels and handle facilitate elevating one end of the stand and machine relative to the underlying support surface such that the stand and machine are supported by the wheels for movement from one location to another. When unfolded, the wheels and handle engage the underlying surface to support the threading machine in an elevated use position. Stands of this character are disclosed, for example, in U.S. Pat. Nos. 4,611,823 to Haas and 5,087,013 to Gress et al.
While wheeled stands of the foregoing character adequately serve their intended purpose with respect to supporting a threading machine in an elevated use position and facilitating the transportation of the machine from one location to another when the stand is in the folded position, there are a number of disadvantages with respect to the spring and screw arrangements by which the stand and the machine mounted thereon are displaced between the folded and unfolded positions of the stand. In this respect, the threading machine is quite heavy and may for example weigh 100 to 200 pounds. Therefore, in a counterbalancing spring arrangement such as that disclosed in the aforementioned patent to Haas, the spring force required to facilitate displacement of the stand and machine between the folded and unfolded positions of the stand is such that the latter operations are hazardous to a workman and can lead to injury. In particular in this resect, the spring is tensioned when the stand is in the folded position and, even though this tension is opposed by the weight of the machine during displacement of the stand to the unfolded position, the displacing force is not uniform and it is difficult for the workman to control unfolding of the stand so as to preclude sudden upward extension of the stand in response to contraction of the spring. An especially hazardous condition exists if the workman forgets to or inadequately latches the stand in the folded position and then attempts to remove the threading machine from the stand. This can result in uncontrolled accelerated displacement of the stand to the unfolded position subjecting the workman to serious injury. Still further, the counterbalance spring is contracted when the stand is in its unfolded position and, even though the weight of the machine is applied to the stand so as to apply an extending force on the spring, considerable physical effort is required on the part of a workman to initially displace the stand from the unfolded toward the folded position thereof.
In conjunction with screw operated displacement of a threading machine stand between the folded and unfolded positions thereof, it takes an undesirably long period of time to achieve such displacements and, when the stand is in or near the folded position, the workman has to either bend over or kneel in order to operate the screw mechanism. Such bending over or kneeling together with the time and effort required to operate the screw mechanism can be both physically uncomfortable and tiring for the workman. Still further, the screw mechanism for folding and unfolding the stand is structurally complex and expensive and, due to the weight of the threading machine, considerable wearing force is imposed between the component parts of the screw mechanism, thus increasing maintenance costs in connection with the stand.
A further disadvantage with regard to such stands heretofore available is that they are somewhat structurally complex requiring a support structure for the threading machine in addition to the scissors-like leg assembly by which Such support structure and machine are elevated and lowered as the stand is displaced between the folded and unfolded positions. Such structural complexity adds to the cost of construction as well as the cost of maintenance of the stand.